muscular system

• Smooth muscles are found in the walls of organs and blood vessels and are responsible for involuntary movements.
• Muscle tissue is responsible for movement of the body and its parts and for changes in the size and shape of internal organs.
• Muscle tissue is composed of contractile cells called Myocytes.
• Muscle tissue is classified according to their appearance into striated muscle, in which the cells exhibit cross striations, and smooth muscle, in which the cells do not exhibit cross striations.
• Skeletal muscle is responsible for movement of the axial and appendicular skeleton, maintenance of body position and posture, and help maintain a constant body temperature.
• Skeletal muscle is characterized as tubular, multinucleated, and striated, and is the longest of muscle types.
• Skeletal muscle is voluntary.
• Myoblast are mononucleate precursor cells of skeletal muscle, can differentiate to form multinucleated muscle fibers capable of muscle contraction.
• Muscle fiber contains the usual cellular components, but special names have been assigned to them.
• The sarcolemma forms T tubulues that penetrate or dip down, into the cell so that they come into contact but do not fuse with expanded portions of the sarcoplasmic reticulum.
• The endomysium is a layer of reticular fibers that immediately surrounds individual muscle fibers.
• The perimysium is a connective tissue layer that surrounds a group of fibers to form a bundle or fascicle.
• A fascicle is a functional unit of muscle fibers that tend to work together to perform a specific function.
• Muscle itself is covered by a connective tissue layer called Epimysium.
• Myofibrils are cylindrical in shape and run the length of the muscle fiber.
• The contractile portions of the muscle fibers are composed of bundles of myofilaments.
• Sarcomeres are the portion of a myofibril between two adjacent Z lines.
• Sarcomeres contain two types of protein myofilaments: thick filaments, composed primarily of the protein myosin II, and thin filaments, composed of actin.
• Thick Filaments are composed primarily of the protein myosin II, with the long, rod-shaped tail portion of each molecule aggregating in a regular parallel but staggered array, whereas the head portions project out in a regular helical pattern.
• Thin Filament consists of two intertwining strands of the protein actin, with two other proteins, called tropomyosin and troponin, also present.
• Each thin filament of Fibrous actin (F-actin) is a polymer primarily formed when globular actin molecules (G-actin) join.
• Z disk- Protein fibers that form attachment site for actin.
• H zone is the center of sarcomere.
• I band contains only actin.
• A band is where actin and myosin overlap.
• M line is where myosin are anchored.
• Contraction occurs when action potential travels down the motor neuron to presynaptic terminal causing Ca2+ channels to open, causing Ca2+ to rush into the postsynpatic terminal (depolarization), causing sarcolemma and T-tubules to increase permeability of sarcoplasmic reticulum and release stored Ca2+, causing Ca2+ to bind to troponin which is attached to actin.
• A high percentage of Type I fibers make up the muscles of high endurance athletes such as marathon runners.
• The heart, or cardiac muscle, has one centrally located nucleus/cell, is striated, rich in mitochondria, and has intercalated disks: special cell junctions that allow cells to act as a unit.
• Creatin phosphate is a high-energy compound built-up when a muscle is resting, providing enough energy for only about eight seconds of intense activity, and then it is spent.
• Tone refers to constant tension over a long period of time.
• Tendinitis is inflammation of a tendon due to the sprain of repeated athletic activity.
• Smooth muscle is found on organs, has one centrally located nucleus/cell, is not striated, has less actin and myosin, is under involuntary control, and is different from cardiac muscle in that it does not have intercalated disks: special cell junctions that allow cells to act as a unit.
• Hypertrophy or Muscle growth refers to an increase in muscle mass.
• Type IIa fibers contain many mitochondria and high myoglobin content, are capable of anaerobic glycolysis, and make up fast-twitch, fatigue-resistant motor units that generate high peak muscle tension.
• Cellular respiration, completed in mitochondria, usually provides most of muscle’s ATP.
• Acetylcholinesterase is released and Na+ channels close and contraction stops.
• Strain is the overstretching of a muscle near a joint.
• Spasms are sudden and involuntary muscular contractions, often accompanied by pain.
• The bending forces actin to slide over myosin.